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B-XRD 1043
Analysis of powder crystal structures of organic
crystals using a high-resolution convergent beam
optical system
Introduction
Previously, it was typical to conduct crystal structure analysis using the single crystal method. However, analysis of crystal
structure using the single crystal method is difficult in the case of samples for which it is hard to produce single crystals,
and samples for which crystal growth is difficult even if single crystals can be produced. In recent years, the precision of
powder X-ray diffractometers has been improving, and thus it is becoming possible to conduct crystal structure analysis
using powder samples. Here we show an example where a powder sample was measured, and structural analysis was
conducted based on the obtained diffraction pattern.
Measurements and results
The crystal system of γ-indometacin crystals belongs to the triclinic type, and thus many diffraction lines overlap, and it is
difficult to determine the lattice constants from the powder X-ray diffraction pattern. Fig. 1 shows an overlay of the X-ray
diffraction pattern obtained with a high-resolution convergent beam optical system, which enables linear focus using an
elliptical surface multilayer mirror of monochromatized X-rays only on CuKα1, in a Ge (111) Johansson-type curved
crystal; and the X-ray diffraction pattern obtained using a conventional parallel beam optical system containing CuKα1 and
Kα2 lines. With the data measured with the high-resolution convergent beam system, it can be easily confirmed that there
are minute, strongly overlapping peaks which were difficult to discover with the conventional optical system. The structure
was successfully determined due to this improvement in data quality.
Intensity (a.u.)
― Parallel beam
― Convergent beam
10
15
2θ (°)
20
25
Fig. 1: Measurement data for γ-indometacin obtained with a conventional parallel beam optical system (red, upper
pattern) and a high-resolution convergent beam optical system (blue, lower pattern) (The arrow marks indicate
peaks which cannot be detected with a parallel beam optical system)
The initial structure was determined using the
direct-space method (parallel tempering method),
and the structure was refined using the Rietveld
method. The crystal structure obtained through
refinement exhibited a good match with the structure
obtained using single crystal structure analysis, as
shown in Fig. 2.
Fig. 2: Crystal structure of γ-indometacin obtained from
powder crystal (yellow) and single crystal (orange)
Recommended equipment and software
®
► Automated Multipurpose X-ray Diffractometer SmartLab + Kα1 Optics + Ellipsoidal multilayer X-ray mirror (CBO-E) + High-speed 1D
detector D/teX Ultra + Integrated X-ray Powder Diffraction Software PDXL
(L0519en)